Heat exchanger



July 8, 1952 DAWSON 2,602,877

HEAT EXCHANGER Filed July 22, 1950 2 SHEETS-SHEET 2 INVENTOR.

fled C. Dawon Patented July 8, 1952 OFFICE HEAT EXCHANGER Fred C. Dawson, Canton, Mass.

Application July 22, 1950, Serial No. 175,396

12 Claims. (01. 219-39) This invention relates to heat exchangers, and relates more particularily to heat exchangers utilizing electric heaters for superheating steam, which is used for duties such as drying of printed sheets and the fusing of plastics.

My Patent No. 2,464,119 which issued March 8, 1949 discloses a dryer in which superheated steam is' projected within a hood upon the upper surface of a sheet having printing thereon of moisture setting ink. This invention provides an'improved heat exchanger for superheating and applying the superheated steam to the surfaces of materials to be heated by the steam, and which maybe used not only for drying, but for heating; aside from drying, as for the fusing of plasticsfiw L A'fe'atu're'of the invention resides. in the effective use of electric heaters for the superheating of steam. This is accomplished, in one embodiment ofthe invention, by not only passing the steam to be superheated, longitudinally of a pipe around a centrally disposed electric heating element, but by providing a tube wound spirally around the heatingelement in contact therewith and with the interior of the pipe, whereby not only is extended heat exchange surface provided, but turbulent steam flow as well, the latter breaking' up theinsulating films which tend to'form on heat exchange surfaces.

An object of the invention is to provide an improved heat exchanger particularly suited for the superheating ofsteam. I

Another object of the invention is to provide an improved heat exchanger utilizing electric heating elements for the heating of a gas such as steam. j

Another o'bject'of the invention is to provide an improved thermostatic control for the regulation of heat applied by an electric heater to the heating of a gas1 such as steam.

The invention will now be described with reference to the drawing, of which: Fig. 1 is a side elevation, partially in section, of :a heat: exchanger embodying this invention,

Fig. 2 is a plan view looking downwardly upon the heatexchanger of Fig-. 1;

--Fig. 3. is a sectional view along the lines 3-3 ofFig.1; H v

Fig. 4 is apartial plan view, partially in section, and partially broken away to show the location of a thermostatbulb in one of the heat exchangers; f

Fig. 5 is a section along the lines 5-5 of Fig. 4;

Fig.6 is a side elevation of another heat exchanger embodying this invention, and difiering from that illustrated by Figs. 1 and 2m that a single tube containing an electricelement, instead of a pair of tubes containing electric heating elements, is used, and

Fig. 7 is a partial side elevation of one of the heat exchangers and illustrates one of the stepped, rotary plates which is used for adjusting the steam flow to suit different widths of sheets being treated.

Mysaid patent may be referred to for the illustration of a hood and its accessoriespfor placement over a'surface to be heated. Such a hood would be used over the heat exchangers illustrated by the present drawing.

Referring first to Figs. 1, 2 and 3, the heat exchanger illustrated is supported from the structural angles I0 and II which extend above'and on opposite sides of a surface to be heated.

The heat exchanger comprises the steam distributing pipe I2 having closed ends I3 and I 4, and having a narrow slit or spaced nozzles I5 (Fig. 3) in its lower center and through which, superheated steam is projected upon a surface to be heated. The metal bar I6 extends horizontally across the end I3 of the pipe I2 and is attached thereto as by welding. The bar I6 is attached to the angle ID by the bolts IT. The rods I8 are attached as by welding, to the pipe I2 adjacent its other end, and are slidably fitted with circular openings in the angle I I for provid-- ing expansion movement when heat'is applied.

The pipe I2 has attached to the opposite sides of its upper portion, as by welding, the two tubes 20 and 2I which are interconnected at their ends adjacent the end I4 of the pipe I2, by the tube 22 extending transversely therebetween. Steam from a conventional source is supplied through the piping 23 into the interior of the tube 20. The tube 2I and the pipe I2 have a commoninterconnecting slot 24 adjacent the left hand end of the tube 21 for supplying superheated steam from the tube 2I into the pipe I2. I

Each of the tubes 20 and 2| contains a centrally extending, cylindrical, electric heating element 25 having the connection 26 at its ends for the supply of electric energy. A tube Zlis wound spirally around each element 25 incontact with its outer surface, and in contact with the inner surface of the tube 20 or 2I in which it is placed. The tubes 20 and 2! preferably are flattened where they touch the tubes 21 as illustrated by Fig. 3 of the drawing, for providing better contact with the tubes 21. The tubes 21- also serve to support and center the heating elements 25 in the tubes 20 and 2I. a

The ends of the elements 25 are held in the threaded rods 29 on which the nuts 39 are threaded against the ends of the tubes 25 and 2|, for securing the elements in place within the ends of the tubes. An assembly consisting of an element 25 and a tube 2'! wound thereon can be slid into a tube 26 or 2i through one of its ends. The rods 29 have the sleeves 3| threaded thereon inside the end portions of the tubes andZI and which serve to; space the rods 29 andthe elements from the walls of the tubes 25 and 2 I, and since they are slidably fitted in the ends of the tubes 20 and 2|, they provide for outward movement of the ends of the elements when they expand on being heated.

Each distributing pipe I2 has two pairs of Cil cular openings in one lower side, one pair adjacent each end, and through which extend the bolts 32 having the wing-nuts 33 threaded therer on. A parti-cylindrical plate 34 has a, pair of slots 36 therein around the pair of bolts 32 adjacent-one end of the pipe I2, and another particylindrical plate has apair of slots 31 therein around the pair of bolts 32' adjacent the other end of the distributing pipe.

The plates 34 and'35'arecurved to fit against the exterior surface of the distributing pipe, and are movable upand down by positioning the slots therein relative the bolts 32 when the wingnuts 33 are loosened and serve to block oil sufficient of thesuperheatin steam discharge nozzles I5 tosuit the widthof the surface to be heated.

'When the surface to beheated has maximum width requiring all of the nozzles of thedistributor pipes to be in operation, the plates 34 and 35'will be raised to their uppermost positions so that no nozzles are blocked. When a surface to be heated is narrower than maximum, the p'lates34 and 35 are lowered to blockoff suiiicient'of the nozzles to suit the width of the surface. This is accomplished through the stepped construction of the lower edges of the plates. As illustrated by Fig. '7', the plate 34 has stepped horizontal, lower edges 45, 4! and 42, the outer edge 40 being lowermost, the intermediate edge 4| being higher than the edge 45, and the inner edge 42 being higher than the edge 4 I.

' Likewise, the plate 35 has the stepped, horizontal lower edges 43, 44 and45, the outer edge 43being lowermost, the intermediate edge 44 being higher than the outeredge 43, and the inner e'dge45 being higher than the edge 44.

For a maximum width surface to be heated, the 'plates 34 and 35 are raised to their uppermost positions and the wing-nuts 33 are tightened to hold them in that position. At such time, none of the nozzles I5 are blocked, and superheated steam isapplied from all the nozzles.

When a surface having a width less than the said maximum width by a dimension equal'to the added lengths of the-plate edges 43 and 43 is encountered, the plates 34 and 35 are lowered so that the outer nozzles I5 are blocked by the outer plate edges 45 and 43. 7

When a surface having a width less than the maximum by a dimension equal to the added lengths of the'plate edges 40, 4|, 43 and 44 is encounteredthe plates are lowered further until their edges 4| and 44 block oif more of the nozzles. T

Whena surface having 'a minimum Width is encountered, the plates are lowered still further until the plate edges 42 and 45 block off still more'of the nozzles.

In the operation of the heat exchanger illus- 4 trated by Figs. 1, 2 and 3, electric heat is applied to the heating elements 25, and steam is supplied through the piping 23 into the interior of the tube 25. The steam is caused by the spirally wound tube 27 to spin around the inside of the tube whereby its interior and the exterior of the element 25 are effectively scoured for preventing the formation of insulating steam layers. The

tube 2 1 als o provides extended heat transfer surface for f facilitating the superheating of the steam; On reaching its right hand end of the tube 25, the steam passes through the crossconnecting tube 22 into the interior of the right hand end of the tube 2|, and passes along the length of the tube 2| around a heating element 25 therein, and is caused to spin around that element by-atube I! wound spirally around same. The superheated steam is then discharged through the slot 24 into the interior of the pipe I2, and is projected from same through the nozzles I5 onto the surface ofthe material being heated,

In the embodimentv of the invention illustrated by Figs..1-3, the steam for each exchanger is superheated first in a tube 20 and then in a tube 2! beforebeing discharged into the distributing pipe [2.

For some duties-where such a high degree of superheat is not required, theembodiment of the invention illustrated by Fig. 6 maybe used. In this embodiment, a single, exterior tube 20 is used, it being connected adjacent its right-hand end through a connecting tube 45 with a distributing tube 46 within the pipe I2, and having its righthand end welded to the right hand end of the pipe l2. The tube 46 has a slot 41 at its left hand end through which steam is discharged within the'pipe I2. As in the case of Figs. 1-3, the tube 20 of Fig. 6 contains anelectric heating element 25 and a tube 21' Wound spirally therearound.

In the operation of the heat exchanger illustrated by Fig. 6, the steam is superheated in the tube 20 directly by the electric heating element, and is superheated in the tube 46 through the contact of its walls with the wall of the pipe I2, and is discharged through the slot 41 into the interior of the pipe I 2, and from the pipe I2 through the nozzles I5 into the surface being heated.

As disclosed by my patent, several heat exchangers of the type illustrated by Figs. 1-3 or by Fig. 6 are used within one hood. One or more of such heat exchangers preferably each includes a thermostatic control as illustrated by Figs. 4 and 5 of the drawing. A tube 50'extends through'the left hand end of the pipe I2 and a small distance into the exterior thereof, and has the spaced, small inlet openings 5| therein inside the pipe I2. The thermostat bulb 52 is within the tube 50 alongside the openings 5I and exposed to superheated steam entering therethrough. The bulb 52 'has a capillary tube 53 leading through the left hand end of the tube 59, to a bellows which is not illustrated, for actuating an electric switch in the electric supply leads to the connection 25 for the electric heating elements in the tubes 20 and 2 I. The wall tube 50 also contacts the wall of the pipe I 2.

In operation, the bulb 52 responds to the temperature of the steam entering the openings 5 I, and to the temperature of the wall of the tube 58, and acts to disconnect the electric current supplied to the heating elements when the operating temperature has been reached. I

' Where a higher degree of superheat than can easily be provided by the two tubes and 21 with a distributing pipe I2 is desired, another or other similar tubes may be used.

While embodiments of the invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of apparatus illustrated, since modifications thereof may be suggested by those skilled in the art without departure from the essence of the invention.

What I claim as my invention, is H 1. A heat exchanger for heating and distributing a gas, comprising a distributing pipe, means for discharging heated gas longitudinally of the pipe against a surface to be heated, a gas heating tube in contact along its length with the exterior of said pipe, an elongated electric heating element supported within said tube, means for supplying gas to be heated into one end of said tube, and means for supplying heated gas from the other end of said tube into said pipe.

2. A heat exchanger as claimed in claim 1 in which the electric element is in the form of a cylindrical rod, and a relatively small tube is wound spirally around the rod in contact therewith and with the inner surface of the gas heating tube.

3. A heat exchanger as claimed in claim 2 in which the gas heating tube is flattened where it contacts the small tube.

4. A heat exchanger for heating and distributing a gas comprising a distributing pipe, means for discharging gas longitudinally of said pipe against a surface to be heated, a pair of gas heating tubes in contact along their lengths with the exterior of said pipe, an elongated electric heating element supported within each of said tubes, means for supplying gas to be heated into one end of one of said tubes, means for supplying gas from the other end of said one of said tubes into the adjacent end of the other of said tubes, and means for supplying gas from the other end of said other of said tubes into said pipe.

5. A heat exchanger as claimed in claim 4 in which the electric elements are in the form of cylindrical rods and relatively small tubes are wound spirally around the rods in contact therewith and with the inner surfaces of the gas heat ing tubes.

6. A heat exchanger as claimed in claim 5 in which the gas heating tubes are flattened where they contact the relatively small tubes.

7. A heat exchanger as claimed in claim 1 in which means is provided for adjusting the first the interior thereof in contact with the thermostat.

10. A heat exchanger as claimed in claim 1 in which adjusting means is provided for adjusting the first mentioned means for varying the length along the pipe from which gas is discharged therefrom, said adjusting means comprising a pair of curved plates adjacent each end of the pipe, and slidable therearound to partially block the discharge means.

11. A heat exchanger for heating and distributing a gas comprising a distributing pipe,

means for discharging heated gas longitudinally of the pipe against a surface to be heated, a gas heating tube in contact along its length with the exterior of said pipe, an elongated electric heating element supported within said tube, means for supplying gas to be heated into one end of said tube, a second tube within said pipe and having one end adjacent the other end of said first mentioned tube and connected thereto for receiving gas therefrom, and means for supplying heated gas from the other end of said second tube into said pipe.

12. A heat exchanger as claimed in claim ll in which the electric heating element is in the form of a cylindrical rod, and a relatively small tube is wound spirally around the rod in contact therewith and with the inner surface of the gas heating tube.

FRED C. DAWSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,162,537 Yager Nov. 3,0, 1915 1,439,340 St. Clair Dec. 19, 1922 1,460,025 McLean June 26, 1923 1,724,767 Mercer Aug. 13, 1929 1,836,247 Hills Dec. 15, 1931 

